I think it's the random parameter in line 1. Random picks a number between 0 and 1. I don't think the final box does anything. If I am correct, then just change the parameters of the other events from 1, 2, 3, and 4 and change it to ranges, such as 0-.25, .25-.5, .5-.75, .75-1. I think this can replace what you want:
[/] 2 50 [onrelay] [self] [vce_ifval] [<var:br:chance>] [>]
[onvariabletrue] [self] [vce_ifval] [<var:br:chance>] [<=] [.25] [6 7]*
*this is the lines 6 and 7 in you picture, not what the events would be in my example. This should work now.